Green tea

What is green tea and how does it differ from black tea?

Green, black and oolong tea are produced from the leaves of the same plant (Camellia sinensis); the difference is in processing. For green tea the leaves are steamed, pan-fired and dried but not fermented; black tea is fermented and oolong is partially fermented. ^[2] The Ministry of Agriculture and Forestry report on tea production in Türkiye also states that tea is processed in three ways and named black, green and oolong. ^[8]

Polyphenols make up as much as 30% of the weight of dry green tea leaf; most of them are catechins, and EGCG (epigallocatechin-3-gallate) is the most important. The main purine alkaloid is caffeine (2.9–4.2% of the dry leaf). EFSA states that the chemical composition varies greatly with the plant variety, growing environment, season, leaf age and production conditions: EGCG is 1,600–20,320 mg/100 g in dry leaf (13-fold) and 2.3–203 mg/100 g in the infusion (more than 88-fold). ^[1] “The EGCG or caffeine in a cup of green tea” is therefore not a single number.

Is green tea as a beverage the same as an extract supplement?

No. The beverage (infusion) and the concentrated extract in capsules or tablets are assessed separately, in both amount and safety. EFSA states that the mean EGCG amount obtained from green tea infusions in EU adults is 90–300 mg per day, up to 866 mg per day in high consumers, and that supplements containing green tea catechins provide 5–1,000 mg EGCG per day. ^[1]

The main conclusions of EFSA’s 2018 opinion are as follows. ^[1]

• Green tea infusion prepared by the traditional method and ready-to-drink beverages of equivalent composition are generally considered safe according to the “margin of safety” approach, provided intake is at the levels reported in EU member states.
• Even so, rare cases of liver injury have been reported after consumption of green tea infusion; these are most likely an idiosyncratic reaction.
• Green tea extracts (as a beverage or supplement) can be more concentrated, and their composition and form of consumption differ; they cannot be considered safe according to the margin of safety approach.
• In intervention trials, 800 mg or more of EGCG per day as a supplement caused a statistically significant increase in serum transaminases in the treatment group compared with controls.

The NCCIH makes a similar distinction: no safety problems have been reported for green tea as a beverage in adults, but it contains caffeine; liver injury, though rare, has been reported mainly with extracts in tablet or capsule form. ^[2] Details of liver safety in supplements are on a separate page.

Are the benefits of green tea proven?

The NCCIH states that many studies have been done on green tea and its extracts but that no firm conclusion could be reached on whether it is helpful for most purposes of use. ^[2]

The evidence details for green tea and its extracts, with study type and limits for each situation, are on a separate page.

Does green tea help with weight loss?

According to the result of the Cochrane review, green tea preparations produce a small, statistically non-significant weight loss in overweight or obese adults; because the amount of the loss is small, the likelihood of it being clinically important is low. No significant effect was found on weight maintenance either. ^[3] That is, green tea has not been proven to be a “fat burner.” This review was published in 2012 and its searches ended in early 2011–2012; it does not include later trials.

Does green tea harm the liver?

For supplements in extract form, yes, there are reported risks; for the beverage, EFSA reports only rare, most likely idiosyncratic cases. EFSA also states that taking the extract on an empty stomach and as a single dose (bolus) significantly increases the blood EGCG level compared with taking it with food and in divided doses. ^[1] Since 2022, the EU has required a warning “should not be consumed on an empty stomach” on the labels of foods containing extract (extract page). In EFSA’s assessment, 38 intervention trials were examined and it was accepted that taking 800 mg or more of EGCG per day for 4 months or longer is associated with ALT and AST elevation in a small percentage of the population (generally under 10%). EFSA also emphasizes that there is no evidence of liver toxicity below 800 mg per day for up to 12 months, but that an EGCG dose that could be considered safe could not be determined from extracts; serious liver injury was reported at a dose corresponding to 375 mg EGCG per day for a single product containing an 80% ethanolic extract (most likely an idiosyncratic reaction). ^[1]

For the beverage, EFSA states there is no evidence of ALT elevation with consumption of 5 cups or more of green tea infusion per day (with a 125 mL cup and a mean of 70 mg EGCG/100 g infusion, this corresponds to more than 440 mg EGCG per day). ^[1] For extracts, the dose at which risk occurs varies with the product’s composition and the person’s susceptibility. The NCCIH relays the presence of a gene variant particularly susceptible to liver injury and that 5–15% of Americans carry this variant. ^[2]

Does green tea contain caffeine, can it be drunk in pregnancy?

Yes. 2.9–4.2% of dry green tea leaf is caffeine; the amount in a cup varies with brewing conditions. ^[1] In its 2015 caffeine opinion, EFSA states that caffeine from all sources does not raise a safety concern up to 400 mg per day in non-pregnant adults, 200 mg per day in pregnant women, and a single dose and daily intake of 200 mg in breastfeeding women; there is not enough information to derive a safe level of intake for children and adolescents; the Panel states that the value of 3 mg/kg body weight/day derived for adults can be taken as the basis for these groups. ^[6] The NCCIH states that in pregnancy caffeine should not exceed a moderate level, and that in breastfeeding very high caffeine intake can cause restlessness and sleep disturbance in the baby. ^[2] These limits are for the total of all caffeine sources; they are not calculated for green tea alone.

Does green tea reduce iron absorption?

Tea and other beverages containing polyphenols can reduce iron absorption. In the study by Hurrell and colleagues in adult volunteers, with a bread meal and radioactive iron, all beverages containing polyphenols reduced iron absorption depending on polyphenol amount: beverages containing 20–50 mg of total polyphenols per serving reduced absorption by 50–70%, and those containing 100–400 mg by 60–90%; the reduction with black tea was 79–94%. Black tea, herbal teas, coffee and cocoa were tested in the study; green tea was not tested as a separate beverage. ^[7] Because the study did not measure green tea directly, the size of the effect for green tea cannot be derived from these data; the iron absorption study done with catechin-containing extract and pure EGCG is on the extract page. For information on iron deficiency, the iron guide can be consulted.

Is there interaction with drugs?

The NCCIH states that high-dose green tea reduced the blood level of the beta blocker nadolol and thus its effect, that green tea extract can reduce the level of the cholesterol drug atorvastatin, and that an interaction with raloxifene (an osteoporosis drug) was shown in an NCCIH-supported study; green tea may also interact with other drugs. ^[2] Details and the numbers from the nadolol study are on the extract page.

Green tea and tea consumption in Türkiye

According to the Ministry of Agriculture and Forestry Agricultural Economics and Policy Development Institute (TEPGE) report, fresh tea consumption per person in Türkiye is 13.7 kg in 2023/24, and the report places Türkiye first in the world in tea consumption per person; dry tea consumption is at the level of 3.5–4 kg. Tea farming is done in the Eastern Black Sea region (Rize, Trabzon, Artvin, Giresun and Ordu); in 2024, about 1.4 million tons of fresh tea leaf were produced and 68% of production took place in Rize. ^[8] The report gives consumption and production data for green and black teas together (under the same GTİP customs tariff codes); it contains no consumption data set aside for green tea.

For this reason, no conclusion on the benefits of green tea can be drawn from total tea consumption in Türkiye. The NCCIH states that green tea consumption has been associated with lower coronary heart disease risk in Asian populations but not in Western populations. ^[2]

In Türkiye, capsules and tablets containing green tea extract can be treated as food supplements under the Turkish Food Codex Food Supplements Communiqué (2013/49); according to the 2013 text of the Communiqué, the label of these products cannot carry a claim of preventing, treating or curing a disease. ^[9] The Ministry’s Restricted Substances List (21/09/2026) limits purified EGCG extract obtained from green tea leaves to 150 mg extract per unit and at most 300 mg extract per day, and requires a statement on the label that more than 300 mg extract per day should not be consumed (03/07/2026); for green tea extract containing non-isolated EGCG, the limit is 540 mg/day of catechins (“kateşin” in the Turkish text), together with other catechins or separately (age 11 and over). ^[10] These numbers are extract or catechin amounts; they are not in the same unit as EFSA’s 800 mg EGCG/day finding. Tea that is drunk does not fall into this category; the distinction is detailed on the extract page.

Who needs additional precautions?

• People using green tea extract or EGCG supplements: According to EFSA, 800 mg/day or more of EGCG as a supplement is associated with increased transaminases; a safe dose could not be determined from extracts. The Health Canada monograph relayed by EFSA asks people with liver disorders to consult a health professional before use and use to be stopped with symptoms such as jaundice, abdominal pain, dark urine, nausea and unusual fatigue. ^[1]
• People with iron deficiency or anemia: tea and other beverages containing polyphenols can reduce iron absorption. ^[7]
• Pregnant and breastfeeding women: the caffeine limit (EFSA: 200 mg per day in pregnancy). ^[6]
• People using nadolol, atorvastatin or raloxifene: the NCCIH reports interactions. ^[2]

This guide does not determine a personal dose, product or medicine interval; the drug’s package leaflet and the physician or pharmacist take priority.